A standard valve or cock of the ball, plug, or slide type has a housing formed on one side with an inlet connection and opposite it on its other side with an outlet connection. These connections open inside the housing at opposite ports in a valve seat on which rides the valve element, the ball, slide, or plug, that itself is formed with a throughgoing passage. In the open position of the valve the valve-element passage is aligned between the two ports for fluid flow therebetween and in the closed position it is not thus aligned so that no fluid can flow between them. At intermediate positions the valve element and the seat at the outlet form a throttling gap that creates turbulence and a pressure drop due to the Carnot effect and that causes erosion of the valve element and/or of the seat, and/or of the outlet connection.
As described in German patent 3,803,417 filed 05 Feb. 1988 it is known to line the passage of the valve element with a wear-resistant material like sintered ceramic. Nevertheless there is erosion at the throttling gap that reduces the service life of the valve if it is used as a throttling-type metering valve.